Last month, more than 40 of Kenya's athletes were subjected to out-of-competition blood tests in their home country for the first time after a team of drug testers descended on the Rift Valley, a long-time magnet for international distance runners wanting to train at altitude.

The visit by International Association of Athletics Federations testers, which followed pressure from the World Anti-Doping Agency in the wake of claims made by a German TV documentary last year that Kenyan doctors were dispensing performance enhancing drugs, were just the latest reminder that doping suspicions are rarely far away in track and field.

Ever since the fallout from Ben Johnson's failed test at the Seoul Olympics in 1988, the sport has been viewed with an understandably cynical eye. Wada's director general, David Howman, has again stoked those concerns by telling the Guardian that it is the governing body most likely to turn out to be "a potential new UCI".

It is a legacy of the sport's history – from Johnson to the Balco scandal, which brought down Marion Jones – that the swirl of rumour is never far away from successful athletes. That history also suggests that testing alone will never be enough to catch those who cheat and, as a truly global sport, track and field is particularly challenged by the need to ensure a level playing field across the world and the complexities and cost of testing and transporting blood.

Howman went on to praise the IAAF for recognising the need for biological passports (it took 3,218 blood samples in 2011) and a clutch of athletes were banned before the London Olympics on the basis of their blood profiles. The samples taken in Kenya by IAAF testers will be compared with in-competition tests for disparities. In 2011, the IAAF conducted 3,704 tests altogether – of which 1,649 were out of competition.

Wada's president, John Fahey, said this week that it had been "concerned for some time" about the Kenyan situation. "The cloud is hanging over their head – the only way to clear it is to properly investigate it. Their reluctance was of concern to us."

On Friday, the three-times 3,000m steeplechase world champion Moses Kiptanui told the BBC that doping was rife among athletes there. "The information shows that there are a good number of athletes out there who are using drugs," said Kiptanui. "All over the world there is corruption in sport. It is not only a matter in Kenya."

Today's champions must pay for the sins of those who came before and Usain Bolt was among those who had to fend off questions during the London Games, criticising Carl Lewis for casting aspersions without making any direct allegations about the Jamaican sprint team. "People doubt us really hard, but we are trying our best to show the world that we are running clean," he said.

Respected figures such as the former Wada chief Dick Pound estimate that the 2% of athletes who are caught cheating is a woeful underestimate. "It's north of 10 and short of 90 [%], but it's more than people expect," he told Sports Illustrated during the London Olympics, after Victor Conte – the man at the heart of the Balco scandal and who now says he is reformed and seeking to clean up sport – put the figure at a shocking 60%.

An academic study by the IAAF and a Swiss laboratory in 2011 put the prevalence of blood doping at between 1% and 48% within different "sub-populations of samples" and an average of 14% – or almost one in seven – across the entire study population. Those figures, combined with its own forthcoming research, are enough to convince Wada that the sport still has a much wider problem than testers can currently establish.

As such, despite its Bolt-inspired wave of popularity on the back of a London Games that put track and field right back in the heart of world sport, adulation will continue to be tinged by scepticism for some time to come.